can you use armor picering with a posion????

Yes, of course you can. Armor Piercing may be put on any character, and whenever that character deals damage (an attack, Poison, Damage Shield feat, whatever), that damage cannot be reduced below one.
A few of the WWChicago Top 8 players used this Armor Piercing Poison idea along with Masterminding damage the Poisoner would take off to another fig (mostly Lockjaw, who Double-Times the Poisoner over to the opposing force right away). This has come to be known as the L.A.M.P. (Lockjaw & Armor-Piercing Mastermind Poisoner) 'strategy'. All perfectly legal.

Absolutely. It's the "in" thing to do!

well, some people do get a little carried away, but sometimes it is the only way to make a figure playable, cartainly some of the earlier poison figures.

Go go Gadget Viper!